Two JBoss Instances on the same server or Double size heap?

I'm using JBoss (v=5.1; OS = CentoOS 5 - 8GB RAM) with the following jvm params:
-Xmx3072m
-Xms3072m
-XX:NewRatio=2
-XX:SurvivorRatio=6
What is the best way to duplicate the number of clients? Two JBoss Instances on the same server or Double size heap?

kri shan wrote:You play around thread parameter settings like maxThreadSize,..

Huh? This advice makes no sense whatsoever. Do you even know how threads are used in a Java EE app server??? Changing thread parameters has no bearing whatsoever on how many apps can be deployed to an app server.

Based on what you wrote, and assuming the the second app has the same usage patterns as the first, then you should just deploy the app to the same instance of JBoss AS. And you could probably decrease the heap size to around 800MB-1200MB and still be OK (my usual guideline is to have 4 times the amount of heap as what is left over after a major collection after the app gets warmed up).